This invention relates to electrodeposition of water dispersed polymers onto a cathode substrate and more particularly to cross-linking said electrodeposited polymers with a reactive bis-maleimide by a combination of heat curing and ultraviolet radiation curing.
Applicant's copending application Ser. No. 595,448 describes an electrocoating composition of a polymer having pendant mercaptan groups in combination with a bis-maleimide cross-linking agent which composition can be electrodeposited onto a cathode substrate. This composition cures upon heating the electrocoated substrate or by ultraviolet irradiation of said electrocoating when an ultraviolet photosensitizer is incorporated into the composition. Ultraviolet radiation curing generally is preceded by lightly heating the electrocoating on the substrate in order to flow-out the electrocoating. The length of time the electrocoated substrate is exposed to the ultraviolet radiation can be decreased by increasing the viscosity or molecular weight of the electrocoating on the substrate.
The present invention takes advantage of the flowing-out step by obtaining a partial cure of the electrocoating during such light heating. Attendant with such partial curing is an increase in the molecular weight or viscosity of the electrocoating which allows a shorter time of subsequent ultraviolet irradiation of the coating to obtain full cure. Shorter total curing time of the electrocoating and total energy savings are thusly obtained.